The invention relates to a method for the operation of a CID sensor matrix in accordance with the "parallel-injection-readout" method.
CID sensor matrices are known and have been described, for example, in the publication "Charge Injection Imaging" ISSCC Digest of Technical Papers, pages 138-139, Feburary 1973, G. J. Michon and H. K. Burke, which illustrates CID sensor matrices of this type constructed in such manner that image points arranged in rows and columns of a matrix configuration are provided on a surface of a substrate comprising doped semiconductor material and including a substrate terminal. Each image point consists of two MIS capacitors which are disposed closely adjacent one another and coupled to each other over the substrate. Such coupling can be so effected that the interspace between the two capacitors is bridged by a zone disposed on the surface of such substrate and doped oppositely thereto, or by a construction in which the interspace between the two gate electrodes of the capacitors is made sufficiently small. In a row of image points, the gate electrode of one of the two image point capacitors of the row is in each case connected to a corresponding row line, and the gate electrodes of the other capacitors are connected to respective column lines associated with each corresponding image point column.
In a simple method for effecting image recording of a CID sensor matrix of this type, all the column lines and row lines are connected to voltages which, with respect to a reference potential across the substrate terminal, are such that depletion zones are produced on the substrate surface at the MIS-capacitors, in which zone the information charge carriers produced by the image light are accumulated and stored. Read-out in such case is effected serially, i.e. image-point-wise, by injecting the stored inversion charge into the substrate and by integrating the substrate current. On the basis of the integrating operation, this method exhibits favorable properties with respect to pulse train input-couplings which disturb the output signal. However, the low cut-off frequency arising from the serial read-out must be deemed a disadvantage.
Higher cut-off frequencies can be achieved by the utilization of the "parallel-injection-readout" method heretofore referred to. This method is described in the publication "Charge Injection Devices for Solid State Imaging", Nato Advanced Study Institute for Solid State Imaging, Sept. 3-12, 1975, Universite Catholique de Louvain by G. J. Michon and H. K. Burke, in which an operating cycle commences with the erasure of the image points, followed by the setting of the store matrix into the image recording state and the read-out. In contrast to the methods heretofore described, in this case the read-out and the erasing operation are separated. The erasing operation is effected by simultaneously connecting all column lines over a suitable device, for example over multiplex transistors, to a voltage which is such, relative to the substrate potential, that any information charges stored in the corresponding capacitors are injected into the substrate. The setting of the matrix into the image recording state is effected by simultaneously bringing the column lines to a bias voltage relative to the substrate potential which is then clamped. Again, this can be effected over the multiplex transistors by connecting suitable voltages thereto. The bias voltage is so selected that a depletion zone (inversion edge layer) exists below the corresponding capacitors. At the same time, all row lines are likewise brought to a voltage which is so selected that a depletion zone (inversion edge layer) exists below the associated capacitors.
With the sensor matrix so set in the image recording state, information charge carriers produced by light accumulate in the depletion zones where they are stored. The read-out now takes place in a row-parallel manner with the voltage on a selected row line being so reduced that the start voltage of the capacitors conncted to such line is almost reached or is even undershot. The information charge carriers stored in the depletion zones of such capacitors are thus moved below the adjacent capacitors associated with the column lines, as a result of which a potential change takes place on the column lines, which change, relative to the bias voltage, is representative of the information stored in the image points of the row. The information thus is now stored in the column lines which can be readily read out by means of suitable devices. The lastmentioned publication refers to a device by means of which the column lines may be read out consecutively, and when the read-out operation has been completed, a new operating cycle commences with another selected row.
While the "parallel-injection-readout" method possesses a high insensitivity to blooming, it has the disadvantage that the operation is not integral. Different pulse train input-couplings during the shifting of the charges and different pulse train input-couplings of the multiplex transistors or of corresponding arrangements occur in the output signal and produce a "fixed noise pattern".